Dynein and the actin cytoskeleton control kinesin-driven cytoplasmic streaming in Drosophila oocytes.

Mass movements of cytoplasm, known as cytoplasmic streaming, occur in some large eukaryotic cells. In Drosophila oocytes there are two forms of microtubule-based streaming. Slow, poorly ordered streaming occurs during stages 8-10A, while pattern formation determinants such as oskar mRNA are being localized and anchored at specific sites on the cortex.

Visualizing the distribution and transport of mRNAs in living cells.

We have visualized the movements of native mRNAs in living cells. Using nuclease-resistant molecular beacons, we imaged the transport and localization of oskar mRNA in Drosophila melanogaster oocytes. When the localization pattern was altered by genetic manipulation of the mRNA's 3' untranslated region, or by chemical perturbation of the intracellular tubulin network, the distribution of the fluorescence signals changed accordingly.

Kinesin I-dependent cortical exclusion restricts pole plasm to the oocyte posterior.

Microtubules and the plus-end-directed microtubule motor Kinesin I are required for the selective accumulation of oskar mRNA at the posterior cortex of the Drosophila melanogaster oocyte, which is essential to posterior patterning and pole plasm assembly. We present evidence that microtubule minus ends associate with the entire cortex, and that Kinesin and microtubules are not required for oskar mRNA association with the posterior pole, but prevent ectopic localization of this transcript and the pole plasm proteins Oskar and Vasa to other cortical regions. Cortical binding of oskar mRNA seems to be dependent on the actin cytoskeleton.